With the recent development of transformation, especially specialized transformation in E. coli K12, an organism which is very well characterized both genetically and biochemically, we have a potent tool to study recombination mechanisms at the molecular level. Products of recombination can be extracted and isolated from the organism and then analyzed for biological activity. We are attempting to study the molecular mechanism of recombination by analyzing the structure and biological function of the products of recombination. Systems have been devised to study both the mechanism of substitution type and addition type recombination. The structure of the products of recombination will be examined by various biochemical and biophysical techniques. The biological function of the possible pre-recombinant and recombinant molecules will be monitored by transformation. We plan to utilize various rec (recombination deficient) mutants in these studies to determine the roles of the three different recombination pathways and the functions of the different gene products in the process of recombination. An effort will be made to develop an in vitro system of recombination. We are also studying the effect of transcription on recombination within the tryptophan operon.